Apparatus for photochemical chlorination reactions



H. M. PITT Jan. 20, 1959 APPARATUS FOR' PHOTOCHEMICAL CHLORINATION REACTIONS Filed Sept. 11, 1956 3 Sheets-Sheet 1 INVENTOR.

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APPARATUS FOR PHOTOCHEMICAL CHLORINATION REACTIONS Filed Sept. 11, 1956 I 3 Sheets-Sheet 2 I rllllnnnanlln H. M. PITT Jan. 20, 1959 APPARATUS FOR PHOTOCHEMICAL CHLORINATION REACTIONS Filed Sept. 11, 1956 3 Sheets-Sheet 5 Patented Jan. 20, 1959 United States atent APPARATUS FOR PHOTOCHEMICAL CHLORINATION REACTIONS Harold M: Pitt, Torrance, Calif., assignor to Stauficr Chemical Company, a corporation of Delaware Application September 11, 1956, Serial No. 609,295

2 Claims. .(Cl. 250-43 The apparatus of the present invention enables hexachlorocyclohexane to be produced continuously in liquid phase, the product resulting directly from the reaction being one containing a relatively high content of the insecticidally valuable gamma isomer of hexachlorocyclohexane, e. g. more than 20% by weight.

It is in general the broad object of the presentinvent1on to provide an improved reactor for the continuous production of hexachlorocyclohexane by the addition chlorination of benzene with chlorine under the influence of actinic light to produce, as a product, hexachlorocyclo hexane having at leasta 20% gamma isomer content.

The invention includes other objects and features of advantage, some of which, together with the foregoing, will appear hereinafter wherein the preferred form of apparatus embodyingthe present invention is disclosed. In the drawing accompanying and forming a part hereof,

Figure l is a side elevation with portions thereof broken away to show some of the operating mechanism.

Figure 2is a bottom plan view of the apparatus shown in Figure 1.

Figure 3 is a section taken along the line 33 in Figure 1, the View being enlarged to show the arrangement of .various of the parts.

Figure 4 is a section taken through one of the circulatmg arms.

Figure 5 is a diagram of a process flow-sheet in which process the present apparatus is particularly useful.

Referring to the drawings, the apparatus comprises a central well 112, having an inlet 113 for the introduction of chlorine and benzene and an outlet 114 provided at the bottom of the central well 112 for removal of a liquid stream containing a product. At its upper end, a

finned pump rotor 116 is provided, this being mounted upon a shaft 117 having a pully 118 at one end, the latter being adapted to be rotated from a suitable prime mover,

not shown.

A plurality of separate U-shaped legs, generally indicated at 121, extend from-the central well 112; in the form'shown, four such legs have been depicted, but more or less can be used as desired, the minimum, of course, being a single leg. Each of the U-shaped legs 121 includes an upper run 122 and a lower run 123 joined by a vertical run 124. Each upper run 122 opens into the central well 112 immediately adjacent the pump rotor 116 and normally receives liquid circulating through the central well 112.

Each of the runs 122 and 123 are made of glass to permit illumination from a suitable light source as lamps 125 to pass therethrough. The lamps are spaced about I the longitudinal axis of each leg and normally extend parallel to such axis, the lamps being surrounded by a suitable reflector housing 126.

Since it is generally preferable to carry out the addition chlorination of benzene at a relatively low temperature, e. g., of the order of 5 C. to -25 C., U-shaped silver tubes 127 (Figure 3) are extended within each of the legs 122 and 123, the ends of each tubes 127 being joined to inlet headers-128and outlet headers 129to permit of the circulation of a suitable refrigerant through each of the tubes 127.

To illustrate practice of the invention utilizing the foregoing apparatus, one can refer to Figure 5 which is a diagram of a flow-sheet which can be employed to practice the invention on a continuous basis. Receiver 6 provides a reservoir for a presently described solvent mixture; the reservoir is kept under a pressure slightly above that of the atmosphere by application of argon, helium or the like through line 7, to ensure oxygen is excluded from the solvent. mixture. A benzene feed line 8 is provided through which fresh benzene is added to replace that whichforms hexachlorocyclohexane; the henzene can be added at any convenient place and it can be added through line 25. Material from the reservoir 6 is drawn out through line 9 under the control of valve 11 into the reactor, generally indicated at 12 and which is likethat described inFigures 1-4 although in Figure 5 it is shown at including only one set of U-shaped legs 121.

The steady state chlorine concentration to be maintained at the temperature of operation is controlled by periodic sampling of the reaction mass, reaction with excess iodide ion, and titration of the sample with thiosulfate solution, a well-known procedure. The steady state chlorine concentration can also be controlled by a photoelectric cell which in turn varies the rate of chlorine supply or the intensity of illumination.

The reactor is maintained at the desired temperature by a refrigerant from source 13. Chlorine is introduced through line 16 while the finned rotor is turned to maintain a homogeneous mass in the reaction zone. Products issuing from the reactor 12 pass through line 1'7 to a secondary reactor 26 (a small pot or vessel whose interior required of the anhydride is to replace that removed with the product and which amounts to slightly less than 1% of the weight of the product.

A packed column section 51 is provided on the solvent preheater 18, the column being equivalent to. at least a single theoretical plate. A reflux condenser 19 is provided above the column 51, thecondenser having a gas vent line Q52 for passing to waste hydro-gen chloride and any. inert gas present. Sufficient heat is supplied to the preheater 13 to maintainsteady state conditions in the column 51. Material from the preheater 18 is taken through line 22 to boiler 23runder the control of a valve 24.

if the concentration in the system of acetyl chloride in relation to acetic acid increases, one can add a small quantity of water to column 51 to hydrolyze the acetyl chloride. In practice, commercial chlorine contains about two pounds or more of water per ,ton and this usually sufficient to care for the acetyl chloride-acetic acid balance.

Materials volatilized in the boiler 23 are sent overhead through line 26 and are condensed by condenser 27 and then fed to a receiver 28 connected by a. barometric leg 29 and a valve 31 to the reservoir 6. .The receiver is kept under a vacuum applied through a vacuum pump (not shown) attached to line 32.

Liquid from the boiler 23 is withdrawn through line 33 under the control of valve 34 and is then passed into a final stripper 36, from which the product isdrawn off through valve 37 and line 38. Solvent mixture from the final stripper 36 is handled through vapor line 39, being passed into condenser 41 and thence into a receiver 42,

t the latter being maintained under a vacuum applied by a suitable vacuum pump (not shown) to line 43. Solvent mixture-from the receiver 42 is withdrawn through 44, under the control of valve 46 and returned to line 24. The solvent mixture collected in receivers 28 and 42 is condensed in an oxygen-free atmosphere.

To illustrate. practice of'the invention utilizing the foregoing apparatus: 23.22 pounds per hour of make-up benzene were added to the reservoir 6, while 2.35 gallons per minute of a benzene-acetic anhydride-carbon tetrachloride mixture were taken off and fed into the reactor 12. 64.08 pounds per hour of chlorine were introduced into the re- 7 P actor 12, which was maintained at a temperature of 10 C. The stream issuing from the reactor 12 contained 2.13 grams per liter of free chlorine. The stream was passed through the secondary reactor 20 to reduce further the free chlorine present by reaction with the benzene. The entie reaction mass stream containing benzene, hexachlorocyclohexane, carbon tetrachloride, acetic anhydride,

acetic acid and acetyl chloride was then sent into the solvent preheater 18, where the material was heated to above its boiling point at the pressure employed, e. g., 92 C. at atmospheric pressure. The composition of the stream in percent by volume, as determined with an infrared spectrophotometer, was as follows:

In the solvent preheater, benzene, carbon tetrachloride, acetyl chloride and acetic acid were volatilized as an azeotrope into a distillation column where the acetyl chloride and acetic acid reacted to form acetic anhydride and hydrogen chloride. The anhydride was returned to the still preheater and the hydrogen chloride removed through an overhead gas line.

In the example, 0.32 pound of hydrogen chloride was {taken ofi per hour. The composition of the material pass- 'ing' through line 22 was essentially the same as that enter- .ing'the preheater bceause the change in composition effected in column 51 was too small to measure by usual analytical methods. The efiect of the heating-distillation step can only be observed after some period of operation for, in the absence of the heating-distillation step, a gradual decrease occurs in the acetic anhydride concentration, while theconcentrations of acetylf chloride and of acetic acid increase. I v r The material in line 22 passed under the control of valve 24 to the boiler 23 where the solvent mixture was vaporized and taken overhead through line 26 to the condenser 27. The receiver 28 was maintained at a pressure of -200 mms. of mercury- The solvent mixture was returned through the barometric leg 29 to the reservoir 6.

stantially parallel elongated transparent tubes, cooling ingfend of the fourth tube opposite said pump rotor. i

The liquid collected in boiler 23 was passed through line 33 into the final stripper 36 where the solvent mixture present was removed through line 39 to receiver 42; 86.66' pounds per hour of product were also taken ofi the stripper 36, of which 24.3 pounds were the gamma isomer of hexachlorocyclohexane, a 28.0% gamma isomer content. Receiver 42 was maintained under an absolute pressure of 25-35 mms. of mercury. The product contained 0.69 pound of acetic anhydride; an equal amount of acetic anhydride was added each hour to line 25. Y

The product taken off through line 38 was liquid .andv at a temperature of C. It was stirred vigorously with water to remove the trace of acetic anhydride present and to form the material into fine pellets.

From the foregoing, I believe it will be apparent that I have provided a novel, simple and improved reactor for the continuous chlorination of benzene to produce hexachlorocyclohexane having an increased content of the gamma isomer.

I claim:

1. A reactor consisting essentially of a. pair of submeans extending longitudinally within each tube, actinic light sources cooperatively adjacent the outer surface of said tubes, a third tube connecting said pair of tubes atone end thereof, a fourth tube connecting said pair of tubes at their other end, a multi-vane centrifugal pump rotor in said fourth tube for circulating liquid through one of said pair of tubes and then through said third tube and then through the other of said pair of, tubes and back to said fourth tube, means for introducing a make-up stream of Y reactants into the circulating liquid issuing from said other tube into the fourth tube, and means for withdrawing a stream of the liquid as a product carrying stream from the end of the fourth tube. v I a t 2. A reactor comprising-a pair of substantially parallel elongated transparent tubes, cooling means extending 1ongitudinally withineach tube, actinic light sources coopera tively adjacent the outer surface of said tubes, a third tube. connecting said pair of tubes at one end thereof, a fourth tube connecting said pair of tubes at their other end and extending on each side thereof, a 'multi-vaned centrifugal pump rotor provided at one end of said fourth tube for circulating liquid through one of said pair of tubes and then throughsaid third-tub'e and then through the-other, one of said pair of tubes and'back to said fourth tube, means forintroducing a make-up stream of reactantsiint the circulating liquid issuing from the said other tube into the fourth tube, andmeans for withdrawing a stream of the liquid as a product carrying stream from the extend- References Cited in the file. of this patent -UNITED STATES PATENTS 2,436,366 Sconce et al Feb. 17, 194 8 2,499,129 7 Calfee et a1. Feb.28,' 1950 2,572,913 Calfee et al. Oct. 30,195; 2,608,660 Noebels Aug-'26, 1952, 2,622,205 Miller et al. Dec. 16, 1952' 2,662,186 Governale et a1; Dec. 8 1953 3 2,688,592

Skeeters et al'. Septi;7,f 19 5 4 

1. A REACTOR CONSISTING ESSENTIALLY OF A PAIR OF SUBSTANTIALLY PARALLEL ELONGATED TRANSPARENT TUBES, COOLING MEANS EXTENDING LONGITUDINALLY WITHIN EACH TUBE, ACTINIC LIGHT SOURCES COOPERATIVELY ADJACENT THE OUTER SURFACE OF SAID TUBES, A THIRD TUBE CONNECTING SAID PAIR OF TUBES AT ONE END THEREOF, A FOURTH TUBE CONNECTING SAID PAIR OF TUBES AT THEIR OTHER END, A MULTI-VANE CENTRIFUGAL PUMP ROTOR IN SAID FOURTH TUBE FOR CIRCULATING LIQUID THROUGH ONE OF SAID 